Visual art review: British Art Show 7: In The Days Of The Comet

There are a few stand-out pieces in this show sprawling across three venues but a look behind the curtain shows much of the rest can't put its money where its mouth is

• Christian Marclay's The Clock

British Art Show 7: In The Days Of The Comet

CCA, Tramway and Gallery of Modern Art, Glasgow ***

THE British Art Show used to be for up and coming young artists, but for British Art Show 7 the age range has widened. The show is quinquennial and it also tours, so it has come to Glasgow, split between CCA, the Gallery of Modern Art (GoMA) and Tramway. There are 39 artists and the selectors have taken the title of HG Wells's In the Days of the Comet as subtitle to the show.

There are no obvious comets in the heavens just now, but the blurb explains: "The exhibition uses the motif of the comet – with its allusions to the measuring of time, the recurrence and renewal of forms and ideas, portents and omens, and parallel universes – to trace a path through current preoccupations in art." As beauty is said to be in the eye of the beholder, here, I fear, coherence is only in the eye of the selectors. The show seems to be just the usual random mix.

The first thing that greets you at the CCA is a selection of Alasdair Gray's portrait drawings. After his great success as a novelist and long neglect as an artist, he has come from behind finally to achieve recognition. Nevertheless, it is a surprise to find him here. Simon Martin, hanging alongside, is much more typical of the British Art Show.

He has borrowed an Olmec idol with its display case from the Sainsbury Centre and hung photographs of a grid construction by Sol Le Witt beside it. We are told, earnestly, that his topic is how art is presented in museums. If that is so, he is in the wrong business.

Wolfgang Tillmans, an artist with a big reputation, has most of the main gallery. A big green photograph dominates the end wall. Tables are set out in front with a miscellany of press cuttings and photos.

Called Freischwimmer – "Free Swimmer" – the big photo is made with light directly onto photographic paper. The effect is like a cloud of green gas. It seems to be where the idea for the Day of the Comet theme comes from as the catalogue gives a long quote from Wells's novel about the comet filling the sky with green light. It then goes on rhapsodically to explain, apropos the big photo and the assorted press pictures, that "Tillmans uses photography to identify a space between doubt and belief, pointing to the dangers of claims on truth, and exploring how culture and history develop from systems of received knowledge". The first part of that statement is meaningless, the second obvious. As so often in this kind of art, the image is supplanted by the words explaining it; reading upstages seeing. It is not so much the oft-cited Emperor's new clothes that one thinks of here, as the Wizard of Oz: an ordinary, unimpressive voice amplified from behind a grandiose but very flimsy screen.

Anja Kirschner and David Panos present The Empty Plan, a feature-length film about Brecht in Hollywood. It begins with Brecht typing a screenplay.

Halfway through someone asks: "What happened to the screenplay?" Good question. It is no doubt an interesting subject, but it's in the wrong place. It should be in the cinema.

However, the most impressive presentation at the CCA is Christian Marclay's 24 hour film, The Clock. Nobody is expected to watch it right through, but sampling it is fun. It is a collage of bits of film with clocks in them, stitched together with infinite patience so that, amid constantly changing action and indeed period, the hours and minutes on the countless clocks unfold in real time. It is very watchable and impressive, too, if mostly for the effort it represents.

Where you are subjected so often to tyro film makers, the quality of the clips from which it is composed is a reminder of just how good real film-making is. An intriguing exchange between cinema time and real time, I suppose it also justifies, loosely, the selectors' reference in their introduction to the measuring of time.

At GoMA there is more Alasdair Gray, including his most impressive portrait among those on show, a recent picture called Mary in a Black Dress. The power of Gray's drawing shows up the weakness of Charles Avery's, nearby in yet another big illustration in laboured pencil from his ongoing creation of an imaginary island. Avery also has a big vitrine with life-size figures in another scene from his elaborate, unending fiction. His work is, I suppose, the basis of the selectors' claim to include art that explores parallel universes. Avery's is not a parallel universe, however. It is an unsatisfactory piece of adolescent fantasy.

Coleridge drew a distinction between imagination and fancy: the former powers sympathy, understanding and art; the latter is just making things up. This is fancy.

Nearby Brian Griffiths has made a huge tent that is a canvas portrait of Mickey Mouse. It is refreshingly zany, if not profound. Upstairs, User Group Disco by Elizabeth Price is a lively film that presents all sorts of things as sculpture to a disco soundtrack, interspersed with mock corporate slogans. I particularly liked the politically incorrect Sunny Boy Banana stand and the recherch erotic kitsch with which the film ends.

Michael Fullerton's essays in classical portraiture are also intriguing. He paints with skill and his Trotsky in the manner of Joshua Reynolds is really good.

At Tramway, Sarah Lucas is another of the small group of outstanding artists in this mostly undistinguished company. She has a group of sculptures made from tights stuffed with fluff. They pay homage to Hans Bellmer's unpleasant surrealist dolls and manage to look disturbingly obscene without for a moment being explicit. Alongside her, Maaike Schoorel paints something then paints it out, leaving just a shadow, a fatuous exercise. These artists are in the side room, the only decent space in Tramway. The main tram hall is so big and bald and ugly that it has always defeated any art shown in it. Certainly there is nothing here that could challenge this lugubrious space, particularly when one work by Cullinan Richards, for instance, includes paint pots sitting on the concrete floor and another deploys scaffolding and plastic sheeting, all as though left over by the decorators. Here, among much else, Keith Wilson's Calendar is another variation on a Sol Le Witt grid of cubes, but made of rather hostile looking galvanised steel.

Duncan Campbell makes films "that reactivate arbitrated versions of the past to examine how histories are rehearsed and mediated through contradictory and unreliable representations". Whatever that means, his film Bernadette, about Bernadette Devlin during the Troubles, is a reminder how much of the world's violence stems from self-righteousness claiming sanction from a higher cause.

Finally there is Karla Black, our star at the Venice Biennale. She has a pile of earth like a chocolate layer cake, decorated, it seems, with soap and soap powder. Nearby is a square of powder on the floor with her signature pink plastic around it. Black's materials suggest that she is an imitator of Joseph Beuys. The problem is that Beuys is inimitable. His art takes its whole significance from the aura of his extraordinary personality. Without the aura, it is just so much stuff.

Karla Black has no such aura, so trying to do as Beuys does she is just left with the inert stuff. Nevertheless, for Black, we are told, the "expressive physical engagement with unformed matter prioritises 'material experience over language'". If that sounds as though she thinks she personally invented sculpture, the trouble is that the opposite to what she claims is true. It's the Wizard of Oz again. She is like Tillmans. With the words it generates, her art means very little.

Without them, it means even less.

• Until 21 August